Apparatus for treating slurries

ABSTRACT

De-watering apparatus comprises an inclined hollow perforated tubular member having a slurry inlet at its bottom end. Inside the tubular member, an Archimedian screw is arranged around an upwardly inclined rotatable shaft, and this lifts the slurry which becomes de-watered by the effect of gravity exerted on the raised mass of the slurry. At its upper end the shaft is outwardly tapered to reduce the surface area of the Archimedian platform and thus the slurry volume per pitch which can be carried. A piston is slidably mounted on the upper end of the shaft and exerts a controllable back pressure against the raised slurry, to increase the de-watering effect.

United States Patent 1191 1111 3,921,512 Burns 1 1 Nov. 25, 1975 [54]APPARATUS FOR TREATING SLURRIES 3,092,338 6/1963 Reinhalll 100/117 X3,426,677 2/1969 Combs et al. 100/117 [75] Invent Bums Hurley 3,688,6879/1972 Craig et al. 100/117 England [73] Assignee: Watiord EngineeringLimited, Primary ExaminerPeter Feldman Watford, England Attorney, Agent,or Firm-Mason, Mason & Albright [22] Filed: Mar. 21, 1973 Appl. No.:343,236

[57] ABSTRACT De-watering apparatus comprises an inclined hollowperforated tubular member having a slurry inlet at its bottom end.Inside the tubular member, an Archimedian screw is arranged around anupwardly inclined rotatable shaft, and this lifts the slurry whichbecomes de-watered by the effect of gravity exerted on the raised massof the slurry, At its upper end the shaft is outwardly tapered to reducethe surface area of the Archimedian platform and thus the slurry volumeper pitch which can be carried. A piston is slidably mounted on theupper end of the shaft and exerts a controllable back pressure againstthe raised slurry, to increase the de-watering effect.

1 Claim, 3 Drawing Figures a 68 60 r 70 5a g1; /l52 98- 78 L92 7 \84 54i US. Patent Nov. 25, 1975 Sheet2 of3 3,921,512

i 12/ I GGDQ Nov. 25, 1975 Sheet 3 of 3 3,921,512

US. Patent APPARATUS FOR TREATING SLURRIES The invention relates toapparatus for extracting liquid from slurries, mixtures, suspensions,and the like, all hereinafter referred to generically as slurries, andmore particularly though not exclusively to de-watering apparatus.

According to the invention, there is provided apparatus for extractingliquid from a slurry, comprising means for moving the slurry along aconfined space so as to extract at least some of the liquid from theslurry by the effect of pressure generated within the confined space bythe mass of the slurry, and means for mechanically applying acontrollable back pressure to the slurry at its distal end so as toincrease the effectiveness of liquid extraction.

According to the invention, there is also provided dewatering apparatus,comprising a base supporting an upwardly inclined perforated hollowtubular member, a continuous platform arranged helically about the axisof the tubular member and rotatable within the member about that axis soas to raise a slurry to be dewatered, the volume per pitch of theplatform progressively decreasing towards the upper end of the tubularmember, and piston means movable along the said axis at the upper end ofthe tubular member to apply a variable back pressure to the slurryraised through the tubular member, whereby water is extracted from theslurry by the effect of gravity on the mass of the slurry and thesqueezing action exerted on the slurry by the said back pressure.

De-watering apparatus embodying the invention will now be described byway of example and with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic side view of the apparatus;

FIG. 2A is a cross section through the apparatus of FIG. 1; and

FIG. 2B is an enlarged cross section of the upper portion of FIG. 2A.

The apparatus comprises an inclined hollow rectangular housing 5 mountedon a base 6. Inside the housing are arranged two perforated hollowcylinders 7 (FIG. 2A) each containing a shaft 8 which is rotatablymounted in upper and lower bearings 10 and 12 (the latter may be of thewater lubricated type). At its upper end, each shaft 8 is drivinglyconnected to a respective electric motor 14 through a respective gearbox16 via pulleys 18 and 20 and a belt 22. Only one cylinder and shaftassembly is visible in FIG. 2 and this will be described in detail belowwith its ancillary equipment. The other cylinder and shaft assembly isidentical.

As shown in FIG. 2A, the shaft 8 carries an Archimedian screw or flight24 which thus rotates with the shaft.

The slurry from which the water is to be extracted enters the apparatusthrough a pipe 30 (FIG. 1) and a manually controllable valve 32. Thisleads to an inlet 34 (FIG. 2A) to the interior of the perforatedcylinder 7. At its upper end, the cylinder 7 discharges into a chamber36 through the gap between the top of the cylinder 7 and the undersideof a piston 38. The chamber 36 has a single stock outlet 40.

It will be appreciated that the two perforated cylinder and shaftassemblies have a common pipe 30, valve 32 and inlet 34. In addition, acommon water outlet 42, in communication with a pipe 44 and a valve 46,is provided and is in communication with the space within 2 the housing5 but outside the two perforated cylinders 7.

In operation, in each perforated cylinder 7 the shaft 8 and theArchimedian screw 24 are rotated together by the motor 14 at, forexample, revolutions per minute. The slurry entering via. the inlet 34is carried upwards by the rotating screw 24. As the slurry travels upthe axis of the shaft8 on the Archimedian screw, water drains throughthe perforated cylinder 7 and the slurry thickens. This continuousaction creates a plug of drying slurry within the cylinder and henceincreases the pressure. This increase of pressure causes furtherde-watering, and the thickened slurry then exits from the cylinder 7into the chamber 36 and thence through theoutlet 40. The extracted waterdrops to the bottom of the apparatus and exits via the water outlet 42.

As shown in FIG. 2A, the upper end of the shaft 8 has an enlarged,tapered, cross section given by a built-up portion 50. The effect of thetapered portion 50 is to reduce progressively the surface area on theArchimedian screw 24 towards the upper end of the shaft, thus reducingthe slurry volume per pitch which can be lifted.

The piston 38 (FIG. 2B) is sli dable on the upper end of the shaft 8 butrotates with the shaft, being driven by a key 52 which is screwed to theshaft and engages in a slot 54 in the inner periphery of the piston. AnO-ring 56 makes a seal between the piston 38 and the shaft 8.

The piston 38 presents generally the shape of an inverted cone, and aseries of vanes 58 are bolted to the inverted base of the cone so as torotate, in the chamber 36, as the piston rotates with the shaft 8.

Movement of the piston 38 is controlled by a control piston 60. Thepiston 60 is also of annular form and slides within an annular cylinder62 which is mounted on the underside of the top wall 64 of the chamber36. O-rings 66 and 68 provide seals.

The piston 60 is locked against rotation with the shaft by means of akey 70 which is screwed to the outer wall of the cylinder 62 and engagesin a keyway 72 on the control piston 60. Two rings 74 and 76 which arerespectively fixed (by dowel pins 78) to the control piston 60 and themain piston 38, carry rubbing bearing rings 80 and 82 which thus allowrelative rotation between the two pistons. A bearing ring 84 fixed tothe main piston 38 engages in a circular recess in the control piston 60and locates the two pistons for sliding movement together. The controlpiston 60 is shaped to provide an annular chamber 86 which is incommunication with a lubricating oil inlet 88 through a gap 90 betweenthe inner wall of the cylinder 62 and the shaft 80. By this means, thechamber 86 can be filled with oil, and this oil lubricates the keyway 54and also, via a passageway 92, the bearing rings 80 and 82. In addition,the oil damps the movement of the piston 60. A seal ring 94 seals offthe bearing rings 80 and 82 from the chamber 36. A drain plug 95 may beremoved to drain out the oil.

A tubular shaped bellows 96 is fixed at one end to the outside of thecylinder 62 and at the other end to a ring 98 on the piston 60 and shutsoff the sliding surfaces of the piston 60 from the chamber 36.

The cylinder 62 is pressurized with compressed air through an air inlet100. The compressed air is taken from a suitable compressed air supplyvia a manually controllable valve 102 which feeds to an automaticpressure regulator 104. The outlet pressure of the pressure regulator104 is controlled by a knob 106, indi- 3 cated on a dial 108, andapplied to the cylinder 62 through the inlet 100. A manually operablevalve 110 allows the cylinder 62 to be vented to atmosphere. The

pressure regulator 104 and its associated components are not shown inFIG. 2.

In operation, the pressure applied to the control piston 60 and thecylinder 62 is transmitted to the main piston 38 and causes theundersurface of this piston to generate a controlled back pressureagainst the plug of slurry being raised upwardly by the Archimedianscrew 24. This back pressure very considerably increases theeffectiveness of water extraction in the apparatus, and improves theconsistency of the final output stock. If the slurry plug is lumpy, thenthe automatic pressure regulator 104 allows the pistons 38 and 60 torise, in order to let the lump pass, and the piston 60 then movesdownwardly again, lowering the piston 38.

The vanes 58 which rotate with the piston 38 are advantageous in thatthey help to eject continuously the thickened stock through the outlet40.

It will be appreciated that each of the two cylinders 7 has its own pairof pistons 38 and 60 which are separately controlled.

The housing 5 is provided with an inspection cover 114 which is held inplace by wing screws 116 and can be lifted off after removal of thescrews.

The interior of each perforated cylinder 7 may be inwardly and upwardlytapered instead of or in addition to the taper on the shaft 8. In thiscase, the outer diameter of the screws 24 would be progressively reducedto match.

Although the perforated cylinders have been shown as inclined to thehorizontal, which is the preferred position for low consistencyslurries, the cylinders may instead be arranged at other positionsincluding horizontally. A

What is claimed is:

1. Apparatus for thickening a semi-liquid slurry comprising tubularperforated housing means defining a confined space inclined to both thehorizontal and the vertical and having an inlet at its lower end forreceiving the slurry,

helical screw means for lifting the slurry within the confined spaceaway from the slurry inlet so as to extract at least some of the liquidfrom the slurry by the effect of gravitational pressure generated withinthe confined space on and by the mass of the moving slurry, said helicalscrew means comprising,

rotatable shaft means mounted within the perforated housing meansco-axially therewith, said shaft means having an upper end portionextending beyond the upper end of the perforated housing means, and

a helical thread form fast for rotation with the shaft means, saidhelical thread form defining with the housing means, a helical passage,the cross-section of said passage progressively reducing towards itsupper end,

casing means surrounding the housing means, said casing means havinganoutlet at its lower end for the extracted liquid,

means separating the inlet from the outlet,

means defining a chamber enclosing the upper end portion of theperforated housing means, the upper end of the perforated housing meanscommunicating with the chamber for discharging thickened slurry into thechamber,

means defining an outlet from said chamber,

means located in said chamber for applying a controllable back pressureto the moving slurry so as to increase the effectiveness of liquidextraction, said means comprising,-

first piston means mounted on the shaft means adjacent the upper endofthe housing means, said piston means having a conical surfaceco-axial, with the shaft means, said surface diverging towards the upperend of the shaft means, said surface facing the upper end of the housingmeans and defining therewith anrannular gap leading from the interior ofsaid housing means into the chamber,

means connecting the piston means to the shaft means to permit axialsliding movement of the piston means relative to the shaft means whilerendering the piston means fast for rotation with the shaft means,

second piston means surrounding the shaft means above the first pistonmeans, said second piston means including an annular chamber surroundingthe shaft means,

means defining a cylinder surrounding the upper end portion of the shaftmeans, said cylinder comprising an inner annular wall co-axial with theshaft means, and an outer annular wall surrounding the inner wall andspaced therefrom, the upper end portion of the second piston means beinglocated within the cylinder means between the walls,

means securing the second piston means against rotation with the shaftmeans while'permitting axial movement of the second piston means,

downwardly facing annular bearing means carried by said second pistonmeans co-axially with said shaft means, and V I upwardly facing annularbearing means carried by said first piston means co-axially with saidshaft means, said downwardly facing annular bearing means engaging saidupwardly facing bearing means,

means feeding pressurised fluid to said cylinder whereby said fluidapplies a downwards force to said second piston means, and saiddownwards force is transmitted to said first piston means through saidbearing means to provide said back pressure,

means for adjusting the pressure of fluid fed to said cylinder wherebyto control said back pressure,

and

means for feeding lubricating fluid into said annular chamber defined bythe second piston means, said fluid lubricating the bearing means andacting to damp movement of the second pistonmeans.

1. Apparatus for thickening a semi-liquid slurry comprising tubularperforated housing means defining a confined space inclined to both thehorizontal and the vertical and having an inlet at its lower end forreceiving the slurry, helical screw means for lifting the slurry withinthe confined space away from the slurry inlet so as to extract at leastsome of the liquid from the slurry by the effect of gravitationalpressure generated within the confined space on and by the mass of themoving slurry, said helical screw means comprising, rotatable shaftmeans mounted within the perforated housing means co-axially therewith,said shaft means having an upper end portion extending beyond the upperend of the perforated housing means, and a helical thread form fast forrotation with the shaft means, said helical thread form defining withthe housing means, a helical passage, the cross-section of said passageprogressively reducing towards its upper end, casing means surroundingthe housing means, said casing means having an outlet at its lower endfor the extracted liquid, means separating the inlet from the outlet,means defining a chamber enclosing the upper end portion of theperforated housing means, the upper end of the perforated housing meanscommunicating with the chamber for discharging thickened slurry into thechamber, means defining an outlet from said chamber, means located insaid chamber for applying a controllable back pressure to the movingslurry so as to increase the effectiveness of liquid extraction, saidmeans comprising, first piston means mounted on the shaft means adjacentthe upper end of the housing means, said piston means having a conicalsurface co-axial with the shaft means, said surface diverging towardsthe upper end of the shaft means, said surface facing the upper end ofthe housing means and defining therewith an annular gap leading from theinterior of said housing means into the chamber, means connecting thepiston means to the shaft means to permit axial sliding movement of thepIston means relative to the shaft means while rendering the pistonmeans fast for rotation with the shaft means, second piston meanssurrounding the shaft means above the first piston means, said secondpiston means including an annular chamber surrounding the shaft means,means defining a cylinder surrounding the upper end portion of the shaftmeans, said cylinder comprising an inner annular wall co-axial with theshaft means, and an outer annular wall surrounding the inner wall andspaced therefrom, the upper end portion of the second piston means beinglocated within the cylinder means between the walls, means securing thesecond piston means against rotation with the shaft means whilepermitting axial movement of the second piston means, downwardly facingannular bearing means carried by said second piston means co-axiallywith said shaft means, and upwardly facing annular bearing means carriedby said first piston means co-axially with said shaft means, saiddownwardly facing annular bearing means engaging said upwardly facingbearing means, means feeding pressurised fluid to said cylinder wherebysaid fluid applies a downwards force to said second piston means, andsaid downwards force is transmitted to said first piston means throughsaid bearing means to provide said back pressure, means for adjustingthe pressure of fluid fed to said cylinder whereby to control said backpressure, and means for feeding lubricating fluid into said annularchamber defined by the second piston means, said fluid lubricating thebearing means and acting to damp movement of the second piston means.